Expert says toddler's brain turned into 'mush'

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A paediatric radiologist has told a jury that a 2-year-old's severe head injuries, which resulted in parts of the boy's brain turning into "watery mush", were likely to not have been accidental.

The boy's former stepfather, Peter Ross Moran, 24, is on trial in the High Court in Palmerston North after allegedly causing the damage on May 16, 2011.

The defence says it was either an accident, or the boy's mother, Renee Robinson, caused the injuries.

It is a retrial, after a jury could not agree on a verdict last year.

Yesterday, Crown prosecutor Ben Vanderkolk questioned paediatric radiologist Russell Metcalfe about the extent of the damage to the boy's head.

The boy's skull was fractured, and the whole left side of it was removed at Starship children's hospital to take pressure off the brain.

The brain swelled, causing fluid pockets to close up.

A vein in the brain had been torn and bled into the brain.

Dr Metcalfe said the swelling resulted in blood not making it to parts of the brain, which caused large sections of it to die.

Some of those sections included the left side of the cerebrum - one of the largest parts of the brain - and the cerebellum, which plays an important role in motor control.

Dr Metcalfe said those areas of the boy's brain turned into "watery mush" as they were reabsorbed by the brain.

"Those parts of that brain dissolved away. There was no recovery of those areas."

The injuries to the boy were very common in people who had been in a car crash, but that had not been the case here, he said.

"It was non-accidental trauma which caused severe brain injuries.

"Either his head hit something, or something hit the patient's head."

Notes from Moran's first trial show Dr Metcalfe's opinion has not changed.

Both the Crown and defence agree there was no way to figure out if all the damage happened on May 16 or a few days earlier, when the boy climbed and fell out of the window.

But under cross-examination from defence lawyer Chris Wilkinson-Smith, Dr Metcalfe said the brain bleeding would have started "hours" before he was scanned on the night Moran is alleged to have caused the damage.

Medical experts also scanned the rest of the boy's body to look for other injuries.

Dr Metcalfe said it was done to look for other fractures - which could be a sign of child abuse - but also to look for other explanations for the injuries.